Glass Heart
by thefinalcross
Summary: Rin places his heart – literally – on Haruka's hands. (Just because it's impossible for him to have a heartbeat doesn't mean he can't fall in love. Or so he thinks. But a mermaid's heart is just a useless thing, isn't it?) :: Mermaid AU :: RinHaru, with some MakoHaru, MakoGou and NagisaRei


•••

**glass heart**;**  
**(—a mermaid's heart is a useless thing—)

•••

Nanase Haruka swims to the edge of the Iwatobi border, knowing from the dark tint to the waters that it is currently nighttime for the humans that become so obsessively spellbound once they catch a glimpse of someone like him. Despite it being a time of rest for the barbaric hunters of their kind, Haruka isn't stupid – he knows that it's hardly completely safe for him to venture out. The glimmer of his scales is unfortunately one of the brightest amongst his kind – his grandmother fondly claims that his scales are even brighter than moonlight.

He huffs a little as he remembers that exaggeration but he does duck his head and swims back to the place he calls home.

Once within the vicinity of the unassuming entrance to his home, he adjusts to the water current and swims quieter, because Makoto is a worrywart who will fuss incessantly once he finds out that Haruka sneaked around again to dangerous areas. He knows that his childhood friend is simply being a good friend – the very best friend one could ask for, really – but Haruka will do what he wants to do, and he simply wants to let the water envelop him and carry him to anywhere it wished. He isn't in the mood to allay Makoto's fears about being caught by greedy humans, especially since—

"Yo, Haru," with a voice rough around the edges, Matsuoka Rin makes his presence known as he swims from inside Haruka's own house, moving around as though he owns it.

And that might not be such an overestimation really, judging from what Haruka has heard over the past couple of cycles, what with this generation's queen still unable to bear an heir to the kingdom—

"I told you to wait for me if you're going to swim to the border!" Rin will never admit that he's doing a rather petulant pout, but that's exactly what he's doing. Haruka is a little immune to whining – years of growing up alongside Makoto and Nagisa inevitably prepares one to handle a lot of different things – but he's still working on not making that charming curl of lips leave him completely unfazed. "So where did you swim this time? Is it the North Border?"

Rin isn't a worrywart like Makoto – while it's true that he will whine until the next cycle and maybe even the one after that, he doesn't really stop Haruka from doing what he wanted. Of course, that might just be because Rin enjoys toeing the line between serious danger and thrilling adventure.

"Iwatobi Border," he turns his head pointedly to the side so he isn't receiving Rin's pout at full-blast, "…we agreed to go for the North Border together, didn't we?"

"It's night—" Haruka's head is still turned away, even as he makes his further inside his house that's certainly larger on the inside, but he catches the moment that Rin's reaction to tonight's destination gets swallowed up by his response to Haruka's almost-shy question. "O-Oh, y-yeah, that's r-right."

Haruka thinks he's blushing and the water surrounding them is warm, and Rin is also flushed like one of his grandmother's prized sea rose.

Rin recovers after a few moments, curling his fingers naturally around his forearm, dragging him unceremoniously towards his own bedroom. Haruka doesn't even attempt to invite Rin for a sleepover because that's not how this friendship works – Rin does what he likes, and if he fancies staying over at Haruka's place, then he's only too willing to be imposed on.

•

…his grandmother, Makoto, and Nagisa even – all of their neighbors and even some visitors from far-off places – all of them have something to say about the shimmer covering his scales, on the brilliance coating his movements, on the glimmer concentrating on his tail. He doesn't think it's very special – not to the point that they gush about it – especially since there's one set of scales that he considers to severely outclass his, if he cared about such things.

Rin's scales aren't as overtly bright like his – but his scales look as though there's heartbeat coursing through each fragment, as though there's molten fire simmering just underneath the glass-like surface, as though there's a magnetic force beckoning for one to touch and to _break_ the flimsy barrier between one's fingers and the mysterious flame.

Haruka has never experienced something more beautiful than that.

•

Unlike the tales that have been passed to his young ears by his grandmother, reality isn't so generous with copious amounts of eerie foreshadowing and dark foreboding. The day that Haruka is dreading arrives without a lot of fanfare – well, there _is_ a lot of celebrating and general chaos, but the day doesn't welcome him with thunder roaring in the distance and convenient water storms that leave his breath away.

It's a fairly normal day, all things considered.

Despite the humble-looking entrance of his house, Haruka can actually be considered as someone with a fairly high status, residing in a decidedly noble location. It isn't very surprising to see the King and Queen of the kingdom visiting, but Haruka can already feel the water around him murmur in discontent and disapproval as he stares at the kingdom's sovereign inspect each young mermaid the region has to offer.

Haruka stubbornly turns his head away once he feels the King's scrutinizing gaze land on him, focusing on _willing_ his scales to go dim, just anything so that he isn't noticed. The King is merely looking for _one_ youngster that they can adopt to the royal family and Haruka refuses to part with his home and his friends and—

The day doesn't come with a lot of warning, so Haruka is horribly unprepared when the King easily brushes past him and moves not to Makoto (who's unsubtly hiding behind his back, despite being a good two heads taller), not to Nagisa (whose golden shine rivals the sun on certain days of the week and whenever he gets his way), but to—

"We have found this kingdom's heir!"

Haruka knows that Rin's scales – the pride and life of all the mermaids – are the most beautiful there is. He is quite content to let everyone else be misled into thinking otherwise, but now that the King's wizened eyes have ascertained a similar truth… Haruka is terribly unwilling to let Rin go.

•

He doesn't ask Rin to stay, because Rin does what he likes.

He doesn't plead for Rin to reconsider, doesn't appeal to Rin about a list of pros and cons of abandoning his home for a lavish life at a palace surrounded by strangers who will look at his ruby-red scales and think that there must be something more dazzling than that sight.

He doesn't ask Rin to stay, even if he wants that more than anything else.

•

"This is the last time we'll swim together," Rin says wistfully even as he's smiling like he can't contain his excitement at being chosen as the heir to the kingdom.

Haruka nods stiffly and he feels like his unmoving heart beats for a staggered moment.

He can feel Makoto wavering between pulling him aside to ask what's wrong or keeping quiet instead, while Nagisa chatters about what exciting things await Rin at the palace.

Whether Rin understands the tension is inconsequential, as Rin does what he likes, and this time, he fancies putting an arm around Haruka's shoulders, bringing their bodies close together to the point that their eternally cold skin feels unnaturally feverish even. Haruka knows it's impossible for beings like them to understand the concept of sharing body warmth and stuttering heartbeats – those things only happen in tales passed to him by his grandmother.

"I'll show you something amazing, something you've never seen before," Rin breathes out like a carefully-kept secret against the hair over his ears but he hears each syllable as though it's whispered right into his mind.

Once again, Haruka nods stiffly, because the words that want to tumble out of his lips are words that just cannot be.

•

It's impossible for mermaids to have body warmth – how can that be when they live deep underneath kilometers' worth of water?

It's impossible for mermaids to have blood coursing through their veins – how can that be when their blood is frozen by the cold temperature?

It's impossible for mermaids to have their heart beat like the barbaric humans – how can that be when a mermaid's heart is simply a useless trinket?

But after the race to the North Border and the thrill of almost getting hunted by human mercenaries – Haruka is convinced that there's a heart underneath all of those ruby scales.

•

A mermaid's heart is a useless thing.

Everybody knows that – The Tale of the Fragile Glass Heart is easily the most popular tale to be discussed, re-enacted and criticized within their kingdom. Everybody knows how ridiculously stupid the heroine of that story is for trusting a seemingly honest human with her heart. Everybody knows that the heroine is the ancestor of all the mermaids in the world – but only after her heart was torn out of her still-living body by the monster she thought to be her lover.

But even if it's simply some… _thing_ that doesn't have anything to offer, it's still a good option to have as a memorabilia. For generations, the heart has always been the perfect token to leave to one's important friends. Of course, a simple token doesn't warrant a complete heart so there are quite a number of mermaids that have irregularly-shaped hearts that are incomplete.

…Haruka doesn't know what to do with the complete heart that's in his hands.

But Rin does what he likes – and the gaping hole on his chest will close up in a few cycles, probably even after with the help of the charms inside the palace.

Rin refused to leave a part of his heart on the North Border shrine where they went to earlier and instead only left one blood-red scale – this must be the reason why.

"…Romantic, right?" Rin asks casually, smiling like he isn't leaving any of his friends behind, like he didn't just cut out his whole heart to give to Haruka for safekeeping, like he didn't just imply that there's nobody else he considers important aside from Haruka since he's the only one with a heart on his hands.

Haruka feels his face flush even if it's an impossible thing.

And with his head turned to the side, he catches a glance at the ruby scales that seem to glow even brighter, even without a heart inside Rin's body.

•

"You're _soooooo_ heartless," Nagisa teasingly implores – or is it imploringly teases? – him to be more emotional during their send-off to Rin, but it's difficult in more ways than one, "come _oooooon_."

It's hard to say goodbye as though they won't hear from each other again – there's a Pearl of Clairvoyance that Rin managed to pilfer from his parents—no, just his mother – and that's supposedly powerful enough to cross thousands of kilometers and deliver one's message.

It's also rather tough trying to pretend as though they won't see each other again – there are already deep-set marks on his calendar about the dates and exact times Rin will both visit nearby territories on official business and not-so-official ones.

It's quite challenging to keep quiet about the things Rin told him about – the world above the ocean, the treasures on the unexplored territories, the war with the humans encroaching on the borders, the beautiful sky that's said to be the same color as Haruka's eyes – all while Rin's heart was clutched in his shivering hands. Rin didn't explicitly tell him to keep those things secret, but there's something with the words that made Haruka want to keep them for himself.

Rin is saying something about returning once he's much older and once he has learned all of the palace's secrets to having the most-prized scales in the kingdom, but Haruka simply turns his head to the side because even after all this time, he still cannot fathom how to resist the magnetic charm Rin exudes.

"…Romantic, right?" Rin asks again, as casually as ever, and Haruka nods a little because it is a romantic thing indeed, even if he doesn't understand romance at all.

•

Just because it's impossible for him to have a heartbeat doesn't mean he can't fall in love.

Or so he thinks.

•

…Just like before, the day that Haruka dreads arrives without any sort of fanfare, without any sort of ominous thunderclap, without any sort of vicious storm that threatens to overthrow the order.

Rin arrives – officially during a one-day rest period during the regional inspection done by the royal family; unofficially during a quick retreat after begging an entire line of tutors that he deserves to have a break after six months of nonstop training with the knowledge buried inside the royal library's ancient tomes – with a bodyguard in tow. Said bodyguard has coarse blond hair that's a bloodline trait for strong-bodied mermaids that are rumored to withstand a lightning strike; said bodyguard is perfect with guarding Rin who is now officially the second most important being in the kingdom.

But Rin _is_ Rin and he is Haruka's friend so the two of them meet up on the day that Haruka dreads and anticipates with equal parts.

Makoto has been suspicious for a week now, because fidgeting isn't really his thing but there was an urge to move and to count down that he couldn't quite ignore. Now that Rin is physically in front of him, just a short distance away, the urge to fidget has completely disappeared.

Rin still looks the same but also so different and there's a covering on his scales and that's probably the surprise he told Haruka about and he probably discovered another way to make his scales look even more breathtaking and—

The bodyguard isn't really just a bodyguard after all, because why would royalty simply hire him for his strength? Said bodyguard opens his mouth and delivers the most terrible news—

"This is AMAZING! Those are the most WONDERFUL scales I have ever seen! I have been an advisor for the royal family for almost eight hundred cycles now but I have never seen such MAGNIFICENCE before! Oh you must tell me—"

Haruka can't look away from Rin's face – can't look away from how the longing and excitement splinters into crushing disappointment – can't look away from the realization that Rin brought the royal advisor so that he can show off his achievements at the palace – can't look away from the fact that his mere presence hurt Rin.

And even when Rin rushes off and leaves him behind despite the time they spent together planning their reunion—even when Makoto and Nagisa both find him stone-still with one hand inside the container that has housed Rin's offered heart and the other hand nail-deep in his chest as he was planning to copy Rin's gesture and offer his full heart to welcome him back—even when Rin is long gone—Haruka still can't look away.

•

When Haruka arrives home, there's only one message waiting for him at the Pearl of Clairvoyance:

_Just throw my heart away_.

•

…A mermaid's heart is a useless thing.

•

**END – chapter one**


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